Demand During Lead Time Calculator - Shipping & Logistics Planning

Calculator Inputs

The page uses a single-column content flow, while the calculator area changes to three columns on large screens, two on smaller screens, and one on mobile.

Demand Inputs

Average daily demand Maximum daily demand Demand standard deviation Review period, days

Lead Time Inputs

Average lead time, days Maximum lead time, days Lead time standard deviation Service factor, z

Inventory and Ordering

On-hand inventory On-order inventory Backorders Unit cost Minimum order quantity Order multiple

Reset

Example Data Table

Scenario	Average Daily Demand	Average Lead Time	Demand Standard Deviation	Lead Time Standard Deviation	Service Factor	Expected Lead Time Demand	Reorder Point
Warehouse A	120 units	8 days	18 units	2.1 days	1.65	960 units	1,365.53 units
Warehouse B	85 units	6 days	12 units	1.4 days	1.28	510 units	670.94 units
Warehouse C	210 units	11 days	24 units	2.8 days	2.05	2,310 units	3,623.46 units

These examples show how the reorder point changes when average demand, lead time, or uncertainty increases.

Formula Used

1) Expected demand during lead time

DLT = Average Daily Demand × Average Lead Time

2) Conservative safety stock

Safety Stock = (Maximum Daily Demand × Maximum Lead Time) − DLT

3) Lead time demand deviation

σ_DLT = √[(Lead Time × σ_demand²) + (Average Demand² × σ_{lead time}²)]

4) Statistical safety stock

Safety Stock = z × σ_DLT

5) Reorder point

ROP = DLT + Statistical Safety Stock

6) Inventory position

Inventory Position = On Hand + On Order − Backorders

How to Use This Calculator

Enter average and maximum daily demand based on your shipment or sales history.
Enter average and maximum supplier lead time in days.
Add demand and lead time standard deviations for a more advanced safety stock estimate.
Choose a service factor. Higher values target fewer stockouts but require more inventory.
Enter current inventory, inbound stock, and backorders to calculate the real inventory position.
Use minimum order quantity and order multiple to make suggested orders operationally realistic.
Click the calculate button to display the result section above the form.
Review the chart, result table, and export the summary as CSV or PDF.

FAQs

1) What is demand during lead time?

It is the quantity expected to be used or sold while waiting for replenishment. It helps planners set reorder points that protect against stockouts during supplier transit time.

2) Why is lead time variability important?

Unstable supplier transit times increase uncertainty. Even with steady daily demand, longer-than-expected lead times can exhaust stock sooner, so safety stock should reflect that risk.

3) What does the service factor mean?

The service factor, often called z, links desired service level to safety stock. Higher z values reduce stockout probability but increase the reorder point and working capital.

4) When should I use the conservative method?

Use it when data is limited or when the item is critical. It relies on maximum observed demand and maximum lead time, making it simple and intentionally cautious.

5) What is inventory position?

Inventory position is on-hand stock plus confirmed inbound stock minus backorders. It is more useful than on-hand inventory alone when deciding whether to trigger replenishment.

6) Why round the suggested order quantity?

Suppliers often require minimum buys or carton multiples. Rounding the result makes the recommendation practical for purchasing, warehousing, and transport operations.

7) Can this help with periodic review systems?

Yes. The calculator estimates an order-up-to level for the review period plus lead time. That makes it useful for weekly or fixed-cycle replenishment policies.

8) Is this calculator suitable for all products?

It works well for many stocked items, but very seasonal, intermittent, or highly promotional products may need more specialized forecasting and service-level methods.